A base station apparatus of a wireless communication system for mobile phones etc. sometimes adopts an array antenna capable of directivity adjustment (for example, refer to Patent Literature 1).
An array antenna includes a plurality of antenna elements, and a plurality of phase shifters provided so as to correspond to the plurality of antenna elements, respectively.
The array antenna receives a radio-frequency analog transmission signal given from the outside, distributes the transmission signal into signals corresponding to the plurality of antenna elements, respectively, and radiates the transmission signals into the space via the plurality of antenna elements. The plurality of phase shifters adjust the relationship of relative phases of the plurality of transmission signals, respectively, thereby adjusting the directivities of the transmission signals when being radiated from the plurality of antenna elements.